Editing Randomized controlled trial (section)

== Blinding ==
{{Further|Blinded experiment}}

An RCT may be blinded, (also called "masked") by "procedures that prevent study participants, caregivers, or outcome assessors from knowing which intervention was received."<ref name="Wood-2008" /> Unlike allocation concealment, blinding is sometimes inappropriate or impossible to perform in an RCT; for example, if an RCT involves a treatment in which active participation of the patient is necessary (e.g., [[physical therapy]]), participants cannot be blinded to the intervention.{{cn|date=November 2023}}

Traditionally, blinded RCTs have been classified as "single-blind", "double-blind", or "triple-blind"; however, in 2001 and 2006 two studies showed that these terms have different meanings for different people.<ref name="Devereaux-2001">{{Cite journal |vauthors=Devereaux PJ, Manns BJ, Ghali WA, Quan H, Lacchetti C, Montori VM, Bhandari M, Guyatt GH |date=April 2001 |title=Physician interpretations and textbook definitions of blinding terminology in randomized controlled trials |journal=JAMA |volume=285 |issue=15 |pages=2000–2003 |doi=10.1001/jama.285.15.2000 |pmid=11308438 |doi-access=free}}</ref><ref name="Haahr-2006">{{Cite journal |vauthors=Haahr MT, Hróbjartsson A |year=2006 |title=Who is blinded in randomized clinical trials? A study of 200 trials and a survey of authors |journal=Clinical Trials |volume=3 |issue=4 |pages=360–365 |doi=10.1177/1740774506069153 |pmid=17060210 |s2cid=23818514}}</ref>  The 2010 [[Consolidated Standards of Reporting Trials|CONSORT Statement]] specifies that authors and editors should not use the terms "single-blind", "double-blind", and "triple-blind"; instead, reports of blinded RCT should discuss "If done, who was blinded after assignment to interventions (for example, participants, care providers, those assessing outcomes) and how."<ref name="Moher-2010" />

RCTs without blinding are referred to as "unblinded",<ref name="Marson-2007">{{Cite journal |vauthors=Marson AG, Al-Kharusi AM, Alwaidh M, Appleton R, Baker GA, Chadwick DW, Cramp C, Cockerell OC, Cooper PN, Doughty J, Eaton B, Gamble C, Goulding PJ, Howell SJ, Hughes A, Jackson M, Jacoby A, Kellett M, Lawson GR, Leach JP, Nicolaides P, Roberts R, Shackley P, Shen J, Smith DF, Smith PE, Smith CT, Vanoli A, Williamson PR |date=March 2007 |title=The SANAD study of effectiveness of valproate, lamotrigine, or topiramate for generalised and unclassifiable epilepsy: an unblinded randomised controlled trial |journal=Lancet |volume=369 |issue=9566 |pages=1016–1026 |doi=10.1016/S0140-6736(07)60461-9 |pmc=2039891 |pmid=17382828}}</ref> "open",<ref name="Chan-1995">{{Cite journal |vauthors=Chan R, Hemeryck L, O'Regan M, Clancy L, Feely J |date=May 1995 |title=Oral versus intravenous antibiotics for community acquired lower respiratory tract infection in a general hospital: open, randomised controlled trial |journal=BMJ |volume=310 |issue=6991 |pages=1360–1362 |doi=10.1136/bmj.310.6991.1360 |pmc=2549744 |pmid=7787537}}</ref> or (if the intervention is a medication) "[[Open-label trial|open-label]]".<ref name="Fukase-2008">{{Cite journal |vauthors=Fukase K, Kato M, Kikuchi S, Inoue K, Uemura N, Okamoto S, Terao S, Amagai K, Hayashi S, Asaka M |date=August 2008 |title=Effect of eradication of Helicobacter pylori on incidence of metachronous gastric carcinoma after endoscopic resection of early gastric cancer: an open-label, randomised controlled trial |journal=Lancet |volume=372 |issue=9636 |pages=392–397 |doi=10.1016/S0140-6736(08)61159-9 |pmid=18675689 |s2cid=13741892 |hdl-access=free |hdl=2115/34681}}</ref> In 2008 a study concluded that the results of unblinded RCTs tended to be biased toward beneficial effects only if the RCTs' outcomes were subjective as opposed to objective;<ref name="Wood-2008" /> for example, in an RCT of treatments for [[multiple sclerosis]], unblinded neurologists (but not the blinded neurologists) felt that the treatments were beneficial.<ref name="Noseworthy-1994">{{Cite journal |author-link=John H. Noseworthy |vauthors=Noseworthy JH, Ebers GC, Vandervoort MK, Farquhar RE, Yetisir E, Roberts R |date=January 1994 |title=The impact of blinding on the results of a randomized, placebo-controlled multiple sclerosis clinical trial |url=http://www.neurology.org/cgi/content/abstract/44/1/16 |journal=Neurology |volume=44 |issue=1 |pages=16–20 |doi=10.1212/wnl.44.1.16 |pmid=8290055 |s2cid=2663997 |archive-url=https://web.archive.org/web/20050510212611/http://www.neurology.org/cgi/content/abstract/44/1/16 |archive-date=2005-05-10 |access-date=2010-03-25|url-access=subscription }}</ref> In pragmatic RCTs, although the participants and providers are often unblinded, it is "still desirable and often possible to blind the assessor or obtain an objective source of data for evaluation of outcomes."<ref name="Zwarenstein-2008" />